1. Field of the Invention
This invention relates to electrical connectors such as, for instance, edge connectors for printed circuit boards. In particular, the invention relates to those connectors which are subjected to repeated insertions and extractions of mating connector elements.
2. Description of the Prior Art
Desirable characteristics of electrical connectors include a firm electrical contact between contact elements of the connector and mating contact elements. Printed circuit board edge connectors usually have a large number of contact elements. These elements are simultaneously connected to a corresponding number of contact elements on a circuit board. Often a firm contact force between these elements makes it necessary to apply a relatively large force to insert the circuit board into the connector. Also, there is wear on contact surfaces when the contact elements come together in a sliding motion during the insertion of the printed circuit board into the connector.
In a prior art connector, forces required to insert a circuit board into a connector are reduced by engaging a camming member in the connector housing with the contact elements in the connector. The camming member moves the contact elements out of the way of the board before it is inserted into the connector. After the board has been inserted, the camming member is disengaged from the contact elements. The contact elements are thereby released and make contact with mating contact elements on the board. A relatively small insertion force is required to insert a circuit board into this type of connector. However, the described additional camming operation becomes necessary.
Other connectors use camming members which are operated by the action of the board itself as it is inserted into one of the connectors.
For example, one connector of the prior art has closely spaced camming surfaces located across one another at the opening through which the circuit board is inserted into the connector housing. When the board is inserted into the housing, the camming surfaces ride up on both sides of the circuit board. The thickness of the circuit board spreads the camming members apart. The camming members resiliently spread the housing as well as contact elements located in the housing. Upon full insertion of the circuit board into the housing the camming members become aligned with apertures in the circuit board. The camming members then recede into the apertures to take up their normal, uncammed position; and the contact elements in the housing engage contact surfaces on the board.
Another prior art connector uses a rocker cam to urge initially spaced contacts located in the connector housing into lateral engagement with an inserted circuit board. The cam is activated by the full insertion of the circuit board into the housing. As the circuit board is inserted it spreads closely spaced opposite cam members. These cam members rock or pivot to urge the contacts into lateral engagement with the circuit board.
The latter two connectors reduce wear on electrical contact surfaces by minimizing or eliminating contact engagement forces while the circuit is either inserted into or removed from the connector. The contacts of the connector do not engage the contact surfaces on the circuit board until after the circuit board is almost completely inserted into the connector.
Except when connector contacts are cammed out of the way of a circuit board by a separate operation, the force required to insert the board into its connector is usually related to the magnitude of the engagement force between mating contact surfaces. For circuits where circuit boards or cards are frequently inserted or removed, it is desirable to minimize the force requirements to insert or remove the boards without adding additional camming operations.